i had this problem and an engineer came out(was still under warranty). if you take the lid off and look on the long silver bit in the centre which the air goes into the drum,you can see 2 little brown 'caps' on the top, in the middle of the white 'things'. sorry not very technical. Just push the one on the right down until it 'clicks'. worked for me. Hope it helps.
stephanie, February 2008